Known solenoid pumps use linear springs to bias a plunger against displacement by a solenoid coil in a pumping cycle. When the springs are fully compressed, the springs occupy an undesirably large space since the coils for the springs stack upon each other. Known control schemes for solenoid pumps use a fixed duty cycle, typically 50, regardless of the magnitude of the input voltage to be used to energize the solenoid coils for the pumps. As a result, too little power is delivered to the coils for low values of the input voltage and the coils remain energized even after plungers for the pumps have fully displaced to fully compress the springs for the pumps. As a result, the pumps consume unnecessarily high amounts of energy and undesirable amounts of heat are generated, which degrades operation of the pumps.
Typically, back pressure is present at the outlet port of a solenoid pump and limits operation of the pump, that is, the pump can operate only up to a certain back pressure level. In general, the back pressure works against the spring used to bias the plunger. For example, when the back pressure is greater than the biasing force of the spring, the pumping cycle is terminated (the plunger cannot return to a “rest” position when the coil is de-energized). The known use of linear springs limits the back pressure under which known solenoid pumps can operate. The spring biasing force must be relatively lower to enable the initiation of the plunger displacement when the coil is energized. Since the spring is linear, only the same relatively lower biasing force is available to counteract the back pressure. Known solenoid pumps cannot operate with a backpressure over about 10 psi.
Common rail systems use a relatively low pressure pump to pump fuel from a fuel source to a high pressure pump. The high pressure pump supplies fuel from the low pressure pump to a distribution line, for example, a distribution pipe feeding fuel injectors for an engine. The high pressure pump in a common rail system can operate at pressures of over 29,000 psi. A pressure regulating valve placed between the low and high pressure pumps typically creates a back pressure on the outlet port of the low pressure pump greater than the 10 psi maximum backpressure under which known solenoid pumps can operate. Thus, known common rail systems teach the use of pumps other than solenoid pumps.